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Near-Infrared Properties of Moderate-Redshift Galaxy
Clusters: Halo Occupation Number, Mass-to-Light Ratios and
Omega_m
astro-ph/0703369
Authors: Adam
Muzzin (University of Toronto), H.K.C.
Yee (University of Toronto), Patrick
B. Hall (York University), H. Lin
(Fermilab)
Comments: 18 pages, 6 figures, 2 tables, accepted by ApJ
Using K-band imaging for 15 of the Canadian Network
for Observational
Cosmology (CNOC1) clusters we examine the near-infrared properties of
moderate-redshift (0.19 < z < 0.55) galaxy clusters. We find that
the number of
K-band selected cluster galaxies within R_{500} (the Halo Occupation
Number,
HON) is well-correlated with the the cluster dynamical mass (M_{500})
and X-ray
Temperature (T_{x}); however, the intrinsic scatter in these scaling
relations
is 37% and 46% respectively. Comparison with clusters in the local
universe
shows that the HON-M_{500} relation does not evolve significantly
between z = 0
and z ~ 0.3. This suggests that if dark matter halos are disrupted or
undergo
significant tidal-stripping in high-density regions as seen in
numerical
simulations, the stellar mass within the halos is tightly bound, and
not
removed during the process. The total K-band cluster light (L_{200,K})
and
K-band selected richness (parameterized by B_{gc,K}) are also
correlated with
both the cluster T_{x} and M_{200}. The total (intrinsic) scatter in
the
L_{200,K}-M_{200} and B_{gc,K}-M_{200} relations are 43%(31%) and
35%(18%)
respectively and indicates that for massive clusters both L_{200,K} and
B_{gc,K} can predict M_{200} with similar accuracy as T_{x}, L_{x} or
optical
richness (B_{gc}). Examination of the mass-to-light ratios of the
clusters
shows that similar to local clusters, the K-band mass-to-light ratio is
an
increasing function of halo mass. Using the K-band mass-to-light ratios
of the
clusters, we apply the Oort technique and find Omega_{m,0} = 0.22 pm
0.02,
which agrees well with recent combined concordance cosmology
parameters, but,
similar to previous cluster studies, is on the low-density end of
preferred
values.
CMB Spectral Distortions from the Scattering of Temperature
Anisotropies
astro-ph/0703541
Authors:
Albert
Stebbins
Comments: 17 pages, 1 figure, submitted to Phys. Rev. D
Report-no: FERMILAB-PUB-07-065-A
Thomson scattering of CMBR temperature anisotropies will cause the
spectrum
of the CMBR to differ from blackbody even when one resolves all
anisotropies. A
formalism for computing the anisotropic and inhomogeneous spectral
distortions
of intensity and polarization is derived in terms of Lorentz invariant
central
moments of the temperature distribution. The formalism is
non-perturbative,
requiring neither small anisotropies nor small metric or matter
inhomogeneities; but it does assume cold electrons. The low order
moments are
not coupled to the higher order moments allowing one to truncate the
equations
without any loss of accuracy. This formalism is applied to a standard
Lambda-CDM cosmology after reionization where the temperature
anisotropies are
dominated by the Doppler effect for the bulk motion of the gas with
respect to
the CMBR frame. The resultant spectral distortion is parameterized by u
~ 3e-8,
where in this case u is observationally degenerate with the
Sunyaev-Zel'dovich
(SZ) y parameter. In comparison the expected thermal SZ y-distortion
from the
hot IGM is expected to be >30 times larger. However at z >5 the
effect
described here would have been the dominant source of spectral
distortions. The
effect could be much larger in non-standard cosmologies.
Has PVLAS Detected the Chameleon? hep-ph/0703243 (suggested by
Aaron)
Authors:
Ph.
Brax, C. van
de Bruck, A.-C.
Davis
Comments: 4 pages
We show that the PVLAS anomaly can be understood using a chameleon
field
whose properties depend on the environment. We find that, assuming a
runaway
bare potential V(phi) and a universal coupling to matter, the chameleon
potential is such that the scalar field can act as dark energy.
Moreover the
chameleon field model is compatible with the CAST results, fifth force
experiments and cosmology.
Anisotropy in the Hubble constant as observed in the HST
Extragalactic Distance Scale Key Project results
astro-ph/0703556 (suggested by Scott)
Authors:
M.
L. McClure, C. C.
Dyer
Comments: 23 pages, 5 figures, to be published in New Astronomy
Based on general relativity, it can be argued that deviations from a
uniform
Hubble flow should be thought of as variations in the Universe's
expansion
velocity field, rather than being thought of as peculiar velocities
with
respect to a uniformly expanding space. The aim of this paper is to use
the
observed motions of galaxies to map out variations in the Universe's
expansion,
and more importantly, to investigate whether real variations in the
Hubble
expansion are detectable given the observational uncertainties. All-sky
maps of
the observed variation in the expansion are produced using measurements
obtained along specific lines-of-sight and smearing them across the sky
using a
Gaussian profile. A map is produced for the final results of the HST
Extragalactic Distance Scale Key Project for the Hubble constant, a
comparison
map is produced from a set of essentially independent data, and Monte
Carlo
techniques are used to analyse the statistical significance of the
variation in
the maps. A statistically significant difference in expansion rate of 9
km/s/Mpc is found to occur across the sky. Comparing maps of the sky at
different distances appears to indicate two distinct sets of extrema
with even
stronger statistically significant variations. Within our supercluster,
variations tend to occur near the supergalactic plane, and beyond our
supercluster, variations tend to occur away from the supergalactic
plane.
Comparison with bulk flow studies shows some concordance, yet also
suggests the
bulk flow studies may suffer confusion, failing to discern the
influence of
multiple perturbations.
Supermassive Black Hole Growth and Merger Rates from
Cosmological N-body Simulations astro-ph/0703540 (suggested by
Scott)
Authors:
Miroslav
Micic, Kelly
Holley-Bockelmann, Steinn
Sigurdsson, Tom
Abel
Comments: 12 pages, 8 figures, submitted to MNRAS
Understanding how seed black holes grow into intermediate and
supermassive
black holes (IMBHs and SMBHs, respectively) has important implications
for the
duty-cycle of active galactic nuclei (AGN), galaxy evolution, and
gravitational
wave astronomy. Most studies of the cosmological growth and merger
history of
black holes have used semianalytic models and have concentrated on SMBH
growth
in luminous galaxies. Using high resolution cosmological N-body
simulations, we
track the assembly of black holes over a large range of final masses --
from
seed black holes to SMBHs -- over widely varying dynamical histories.
We used
the dynamics of dark matter halos to track the evolution of seed black
holes in
three different gas accretion scenarios. We have found that growth of
Sagittarius A* - size SMBH reaches its maximum mass M_{SMBH}~10^6Msun
at z~6
through early gaseous accretion episodes, after which it stays at near
constant
mass. At the same redshift, the duty-cycle of the host AGN ends, hence
redshift
z=6 marks the transition from an AGN to a starburst galaxy which
eventually
becomes the Milky Way. By tracking black hole growth as a function of
time and
mass, we estimate that the IMBH merger rate reaches a maximum of
R_{max}=55
yr^-1 at z=11. From IMBH merger rates we calculate N_{ULX}=7 per Milky
Way type
galaxy per redshift in redshift range 2<z<6.
Cosmological Constraints from SDSS maxBCG Cluster Abundances
astro-ph/0703571
Authors:
Eduardo
Rozo, Risa
H. Wechsler, Benjamin
P. Koester, Timothy
A. McKay, August
E. Evrard, David
Johnston, Erin
S. Sheldon, James
Annis, Joshua
A. Frieman
Comments: 10 pages, 6 figures, ApJ Submitted
We perform a maximum likelihood analysis of the cluster abundance
measured in
the SDSS using the maxBCG cluster finding algorithm. Our analysis is
aimed at
constraining the power spectrum normalization $\sigma_8$, and assumes
flat
cosmologies with a scale invariant spectrum, massless neutrinos, and
CMB and
supernova priors Omega_m*h^2=0.128+/-0.01 and h=0.72+/-0.05
respectively.
Following the method described in the companion paper Rozo et al. 2007,
we
derive \sigma_8=0.92+/-0.10$ (1-sigma) after marginalizing over all
major
systematic uncertainties. We place strong lower limits on the
normalization,
sigma_8>0.76 (95% CL) (>0.68 at 99% CL). We also find that our
analysis favors
relatively low values for the slope of the Halo Occupation Distribution
(HOD),
alpha=0.83+/-0.06. The uncertainties of these determinations will
substantially
improve upon completion of an ongoing campaign to estimate dynamical,
weak
lensing, and X-ray cluster masses in the SDSS maxBCG cluster sample.
Cosmological Constraints From the 100 Square Degree Weak
Lensing Survey
astro-ph/0703570
Authors:
Jonathan
Benjamin, Catherine
Heymans, Elisabetta
Semboloni, Ludovic
Van Waerbeke, Henk
Hoekstra, Thomas
Erben, Michael
D. Gladders, Marco
Hetterscheidt, Yannick
Mellier, H.K.C.
Yee
Comments: 14 pages, 6 figures, submitted to MNRAS
We present a cosmic shear analysis of the 100 square degree weak
lensing
survey, combining data from the CFHTLS-Wide, RCS, VIRMOS-DESCART and
GaBoDS
surveys. Spanning ~100 square degrees, with an average source redshift
z~0.8,
this combined survey allows us to place tight joint constraints on the
matter
density parameter Omega_m, and the amplitude of the matter power
spectrum
sigma_8, finding sigma_8*(Omega_m/0.24)^0.59 = 0.84+/-0.07. Tables of
the
measured shear correlation function and the calculated covariance
matrix for
each survey are included.
The accuracy of our results are a marked improvement on previous work
owing
to three important differences in our analysis; we correctly account
for cosmic
variance errors by including a non-Gaussian contribution estimated from
numerical simulations; we correct the measured shear for a calibration
bias as
estimated from simulated data; we model the redshift distribution,
n(z), of
each survey from the largest deep photometric redshift catalogue
currently
available from the CFHTLS-Deep. This catalogue is randomly sampled to
reproduce
the magnitude distribution of each survey with the resulting survey
dependent
n(z) parametrised using two different models. While our results are
consistent
for the n(z) models tested, we find that our cosmological parameter
constraints
depend weakly (at the 5% level) on the inclusion or exclusion of
galaxies with
low confidence photometric redshift estimates (z>1.5). These high
redshift
galaxies are relatively few in number but contribute a significant weak
lensing
signal. It will therefore be important for future weak lensing surveys
to
obtain near-infra-red data to reliably determine the number of high
redshift
galaxies in cosmic shear analyses.
The Cosmic Coincidence as a Temporal Selection Effect
Produced by the Age Distribution of Terrestrial Planets in the Universe
astro-ph/0703429
Authors:
Charles
H. Lineweaver, Chas
A. Egan
Comments: Submitted to ApJ
The energy densities of matter and the vacuum are currently observed to
be of
the same order of magnitude: $(\Omega_{m 0} \approx 0.3) \sim
(\Omega_{\Lambda
0} \approx 0.7)$. The cosmological window of time during which this
occurs is
relatively narrow. Thus, we are presented with the cosmological
coincidence
problem: Why, just now, do these energy densities happen to be of the
same
order? Here we show that this apparent coincidence can be explained as
a
temporal selection effect produced by the age distribution of
terrestrial
planets in the Universe. We find a large ($\sim 68 %$) probability that
observations made from terrestrial planets will result in finding
$\Omega_m$ at
least as close to $\Omega_{\Lambda}$ as we observe today. Hence, we,
and any
observers in the Universe who have evolved on terrestrial planets,
should not
be surprised to find $\Omega_m \sim \Omega_{\Lambda}$. This result is
relatively robust if the time it takes an observer to evolve on a
terrestrial
planet is less than $\sim 10$ Gyr.
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